246
Ind. Eng. Chem. Res. 1994,33, 246-250
Selective Toluene Disproportionation over Pore Size Controlled MFI Zeolite Jagannath Das, Yajnavalkya S. Bhat, and Anand B. Halgeri' Research Centre, Indian Petrochemicals Corporation Limited, Baroda 391 346, Gujarat, India
Selective disproportionation of toluene to p-xylene was studied over modified MFI aluminosilicate. The relationship between extent of silica deposition and para selectivity was established. The effect of reaction parameters such as temperature and weight hourly space velocity (WHSV) on para selectivity was considered. Kinetics of reaction in the temperature range 723-773 K was carried out. The estimated activation energy value is lower than reported for toluene disproportionation in the literature. This has been explained on the basis of enhanced intracrystalline diffusion in the modified zeolite.
Introduction Toluene disproportionation is an important petrochemical reaction to convert low value toluene to higher value xylenes and benzene. Oliver and Inoue (1970) have summarized the research dealing with toluene disproportionation. Commercial processes have been developed using solid acid catalysts by Sinclair/Atlantic Richfield and Toray Industries/Universal Oil Products. Many studies were reported as zeolite-based catalysts to find alternative to Friedel-Crafts or silica-alumina catalysts (Bhavikattiet al.; 1981, Halgeri, 1981; Mavrodinova et al., 1985; Ribeiro et al., 1987; Leu et al., 1990). However, all these large- and small-pore zeolites deactivated with time on stream. On the other hand, medium-pore ZSM-5zeolite was found to be superior in terms of a steady and stable activity for long periods of time on stream and was commercialized in 1975 (Meisel et al., 1977). The absence of bottlenecks in the pore system, high &/A1 ratio, and geometricalconstraint imposed by 10-memberedring pore of ZSM-5 are responsible for a steady life without any deactivation. Moreover, the product stream of toluene disproportionation using ZSM-5 zeolite contained less of undesired CS aromatics as a result of transition-state selectivity. Toluene disproportionation over ZSM-5zeolite is a wellstudied reaction. Kaeding et al. (1981a) and Meshram (1987)have disproportionated toluene to produce benzene and xylenes rich in the para isomer over ZSM-5 zeolites, which were modified with phosphorus, magnesium, and boron compounds. The acid strength distribution and catalytic behavior in the disproportionation of toluene on ZSM-5 zeolites with varying silica-to-alumina ratio and calcined at different temperatures have been studied by Meshram et al. (1983). Structure-selectivity relationship in xylene isomerization and selective toluene disproportionation has been investigated by Olson and Hagg (1984). Nayak and Riekert (1986) and Beltrame et al. (1985) have established the relationship between the catalytic activity and product distribution in the disproportionation of toluene on different preparations of pentasil zeolite catalysts. Effects of carrier gases in toluene disproportionation were studied by Schulz-Ekloffand Jaeger (1987). Shape selectivity of hydrothermally treated H-ZSM-5 in toluene disproportionation and xylene isomerization has been discussed by Kurschner et al. (1990). Effects of crystal size, silicon-to-aluminum ratio, activation method, and pelletization of ZSM-5 zeolite used in toluene disproportionation was covered by Uguina et al. (1991). In general, xylenes produced through disproportionation of toluene over ZSM-5 contained composition near to
thermodynamic equilibrium. Commercially, p-xylene is the most important and desired among the xylene isomers, and efforts are continuously being made to enhance its compositionbeyond thermodynamic value. These include increase in crystal size, incorporation of boron, magnesium, and phosphorous compounds, and poisoning and coking of the external surface sites. Mobil Oil Corporation has developed and commercialized a proprietary catalyst to selectively convert toluene to high-purity benzene and p-xylene. The p-xylene content in xylenes is as high as 95 % , which significantly exceeds thermodynamic equilibrium composition. Among the various techniques employed for achieving very high selectivity, one method which is drawing attention, is the chemical vapor deposition of silica precursor (Niwa et al., 1982; Wang et al., 1988; Halgeri et al., 1991). A para selectivity as high as 98.57 % was attained through this modification during toluene disproportionation (Hibino et al., 1991). In light of published information there is a very good reason to study selective toluene disproportionation over pore-sizeregulated MFI zeolite. We report in this paper (i) silica deposition and its effect on activity and selectivity of MFI aluminosilicate zeolite, (ii)the influence of various reaction conditions on para selectivity, and (iii) the kinetics of toluene disproportionation over pore-size-regulated MFI aluminosilicate.
Experimental Section Materials and Catalyst. Analytical grade toluene (Indian Drugs and Pharmaceuticals Ltd, Hyderabad) and ultrapure hydrogen (Indian Oxygen Limited, Bombay) were used in this study. The catalyst MFI aluminosilicate used in this study was synthesized as per the procedure reported in the literature (Argauer and Landolt, 1972). The occluded organic template in the zeolite was decomposed by calcining in presence of air flow at 813 K for 8 h. It was converted into active proton form by repeated ion exchange with 1 M ammonium nitrate solution followed by calcination at 773 K in flowing air for 6 h. The zeolite was characterized by XRD for phase identification and purity, SEM for crystal size, MAS-NMR for framework composition, and TPD of ammonia for acidity. Silica Deposition. This was carried out in situ by chemical vapor deposition of by bulky silicon compound, tetraethyl orthosilicate. A 6.5 % Si(OCZH5)d solution in 50:50 toluene and methanol was vaporized at 200 O C and passed through the catalyst bed maintained at 503 K. The silica solution was fed at a rate of 8 mL/h, and a flow of
OSSS-5S85/94/2633-0246$04.50~0 0 1994 American Chemical Society
Ind. Eng. Chem. Res., Vol. 33, No. 2, 1994 247 Table 1. Performance Comparison of MFI Aluminosilicate with and without Pore-Size Reduction for Toluene Disproportionation’ catalyst MFI pore-size-regulated aluminosilicate* MFI aluminosilicatec product composition benzene (%) toluene ( % ) p-xylene ( % ) n-xylene ( % ) o-xylene (5%) othersd ( 5% ) performance toluene conversion (wt %) benzene/xylenes (mol/mol) xylene distribution para (96) meta(%) ortho (%)
9.86 77.15 2.91 6.25 2.93 0.90
11.82 76.86 9.03 0.88 0.17 0.26
22.85 1.10
23.14 1.58
24.10 51.66 24.24
88.79 8.65 2.56
Temperature = 773 K Hz/HC = 2. WHSV = 1.52 h-L. WHSV = 0.87h-l. Others are as follows: C144 hydrocarbons,ethylbenzene, and trimethylbenzene.
50 mL/min hydrogen was maintained so that there was uniform contact of the vapor with the catalyst. After the vapor was in contact for the desired number of hours, hydrogen flow was changed to nitrogen. The nitrogen gas was replaced by air and the reactor temperature was raised to 815 K and was kept at this temperature for 10 h to decompose Si(OCzH& to Si02. This procedure results in uniform deposition of silica throughout the catalyst bed. Experimental Procedure. Toluene disproportionation runs were carried out in a continuous, down-flow, fixed-bed reactor at atmospheric pressure. A 1-3-gm sample of zeolite was loaded in the reactor. Before the start of the reaction run, the catalyst was activated at 800 K for 2 h in air to drive off moisture and adsorbed hydrocarbons, if any. Hydrogen gas was used as a carrier gas. The reactant toluene was fed through a Sage syringe pump (model no. 352) into a vaporizer at 423 K, and the vapor was carried by the carrier gas to the catalyst bed maintained at the desired reaction temperature. Product Analysis. The products of toluene disproportionation were analyzed in a Varian Vista 6000 gas chromatograph using a flame ionization detector. The column employed was of 3.2-mm i.d. and 3-m length filled with 5% bentone-34 and 5% DIDP on chromosorb W. Result and Discussion Performance Comparison with and without PoreSize Regulation. A comparison of the performance of MFI aluminosilicates with and without pore-size regulation for toluene disproportionation is presented in Table 1. The pore-size-regulated zeolite exhibited enhanced para selectivity of 89 % at the conversionlevel of 23 % . Benzene formation was slightly higher than that on the unmodified zeolite. A similar trend was observed by Hibino et al. (1991) at very low conversion levels. They reported that the deposition of silica narrows the pore opening size and simultaneously deactivates the external surface, because the inert silica coats the external surface. The para selectivity is enhanced either by narrowing the pore opening size or by inactivation of the external surface. These modifications create additional diffusional constraints for the reactant molecule. Due to this, dealkylation of toluene is increased which results in an increase in the benzene-to-xylene ratio. The change in reduction of pore opening size after silylation was monitored by a standard test reaction. A
100-
1
.! /
c
kl
0
I
I
4
8
12
I
I
16
20
SILICA DEPOSITED ( w t %)
Figure 1. Effect of the extent of silylation on the performance of MFI aluminosilicate for selective disproportionation of toluene: (0) toluene conversion, (a) benzene-to-xylene mole ratio, (x) p-xylene selectivity. Temperature = 773 K; WHSV = 0.87 h-l; HdHC = 2.
mixture of two reactant probe molecules of different kinetic diameter was employed. The reaction mixture contained 50% m-xylene and 50% ethylbenzene. Essentially two reactions take place on ZSM-5 zeolite: (i) m-xylene isomerization and (ii) ethylbenzene dealkylation to benzene and ethylene. As the extent of pore-size regulation by silica deposition increases, the conversion of ethylbenzene is not affected to a great extent but m-xylene conversion drops drastically. With 16 wt % silica deposited ZSM-5 zeolite m-xyleneconversion is only 2 % . While ethylbenzene conversion at the appreciable level. This can be ascribed to the smaller kinetic diameter of ethylbenzene as compared to that of m-xylene and the later value is very close to the pore opening size of unmodified ZSM-5 zeolite. The silica deposition resulted in reduction of pore opening dimension still closer to metaxylene which is why the diffusion of m-xylene inside the channel is affected to a larger extent. Para Selectivity and Silica Deposition. The effect of progressive silylation (extent of pore-size regulation) on toluene conversion and selectivities for benzene and xylenes are reported in Figure 1. Initially up to 8 wt 7’% silica deposition, the conversion of toluene decreased marginally by 3.4%, (from 35% to 31.6%) and also enhancement in para selectivity was marginal (from 23.94% to 26.31%). However after 16 wt % silica deposition, the conversion drops to 23% with a sharp increase in para selectivity to 89%. Further increase in the extent of silylation lowered the conversion and raised the p-xylene selectivity. These results can be explained on the basis that, in the beginning, silica covers only the catalytic sites located on the external surface, thereby reducing the conversion slightly. With increase in silica deposition, the pore openings narrow and the silica layers cover all the external surfaces. Due to this, the diffusional constraints on the reactant and products increases. Toluene conversiondecreaseswhile the para product increases as the isomerization on the external surface decreases. Paparatto et al. (1987) have reported that the para isomer formed selectively inside ZSM-5 channels while isomerization proceeded just on the external surfaces and that the improvement in para selectivity by the modification was due to the inactivation of the acid sites on the external surfaces. In contrast Kim et al. (1989) have suggested that the improvement in para selectivity by the modification of HZSM-5 with oxides was due to the suppression of the isomerization of the primarily produced para isomer. A similar conclusion was also reported by Lonyi et al. (1989).
248 Ind. Eng. Chem. Res., Vol. 33, No. 2, 1994
It has also been reported that selective poisoning of the external surface of zeolite crystallites will improve the shape selectivity of the para isomer (Anderson et al., 1979; Yashima et al., 1981; Nunan et al., 1984). Paparatto et al. (1989) have dealt with the role of the external surface sites in reaction with ZSM-5 catalysts. According to them, on the zeolites samples having larger external surface area, the selectivity to para isomer becomes lower because of the higher extent of the isomerization reaction. The same results can be interpreted in terms of diffusional limitations within the zeolite channels. Kaeding et al. (1981b, 1984) and Young et al. (1982) have investigated not only toluene ethylation with ethylene but also the alkylation of toluene with methanol and toluene disproportionation, comparing the performances obtained on ZSM-5 in proton form and modified by adding P,B and polymeric materials or by coke deposition during the experimental runs. In order to explain the increase in selectivity to para isomers due to these modifications, the authors suggest a mechanism based on the reduction of the dimensions of pore openings and channels sufficiently to favor the formation and diffusion of smallest isomers. However the interaction of modifying agents with the acid sites on the external surface, which reduces the non-shape-selective isomerization, is not excluded. Vayssilov et al. (1993) have reported para-selective alkylation of toluene with methanol over ZSM-5 zeolites. The reactions of toluene alkylation and xylene isomerization are considered both on the external and internal surface catalytic centers of the zeolite crystals. Uguina et al. (1992, 1993) have studied Mg and Si as ZSM-5 modifier agents for selective toluene disproportionation. For both agents, para selectivity corresponding to the primary product was loo%, p-xylene being the unique isomer able to leave the modified pore structure due to the coupled effects of steric constraints enhanced by the modifier agents and the fast internal isomerization. The further decline of para selectivity with conversion is caused by the primary product isomerization on the external acid sites. The best para selectivity-activity relationship obtained with the silicon modification has been assigned to the deposition of this agent on the external zeolite surface, which showed to be in good agreement with kinetic and adsorption-diffusion measurements. Murakami (1989) has investigated the super- selective catalysis by CVD zeolites. This study reports deposition of an ultrathin layer of silica to cover the external surface of zeolites, and the thin layer of silica is effective in controlling the pore opening size without changing the internal structure. Chen et al. (1979) proposed a mechanism for selective disproportionation of toluene. The catalyst with reduced pore size may favor the transfer of a methyl group to the least hindered position of toluene, and the resultant p-xylene formed diffuses out of the pores at a relatively faster rate. In addition, ortho and meta isomers within the pores would isomerize to para as the concentration of the latter is reduced by rapid outward diffusion. With an increase in the extent of silica deposition from 0 to 19 wt %, benzene-to-xylenes mole ratio increased, xylenes selectivity decreased from 52.92 % to 40.3 5% , and toluene conversion decreased from 35 % to 6 % . It is quite indicative from Figure 1that the best results of selective toluene to p-xylene a t appreciable conversions can be obtained from MFI aluminosilicate deposited with 16% silica; therefore, our further studies on pore-size-regulated MFI aluminosilicate was carried out on the zeolite deposited with 16 wt % silica which is designated as 16Si02-AlMFI.
-1
80
60
I
13
25
\ W
6
-2
a
E
' -1
20
7 23
8 03
748 773 T E M P E R A T U R E (OK)
Figure 2. Influence of reaction temperature on catalytic performance of 16SiO.j-AIMFI for selective toluene disproportionation: (0) toluene conversion, (m) benzene-to-xylene mole ratio, ( X ) p-xylene selectivity. WHSV = 0.87 h-l, HdHC = 2.
'
0
8o
°
1
1
t -13
0
1
2
3
4
w
5
SPACE VELOCITY (h-')
Figure 3. Catalytic activity of 16SiO~AlMFIfor selective toluene toluene condisproportionation as function of space velocity: (0) version, (m) benzene-to-xylene mole ratio, (X) p-xylene selectivity. Temperature = 773 K; HdHC = 2.
Effect of Reaction Temperature. Figure 2 depicts the relationship between temperature and catalytic performance of lGSi02-AlMFI. The toluene conversion increased with the increment in temperature from 723 to 803 K, while xylene selectivity decreased and the benzeneto-xylene mole ratio increased. p-Xylene selectivity was affected little up to 773 K above which it was lowered. The main reason for all these observations is increased toluene and xylene dealkylation a t higher temperature. Effect of Weight Hourly Space Velocity (WHSV). The influence of this parameter is summarized in Figure 3. Toluene conversion is lowered from 23% to 9% with change in WHSV from 0.87 to 4.35 h-l, whereas xylene selectivity improved marginally towards para selectivity. Due to a decrease in contact time at higher WHSV, benzene-to-xylenes ratios also showed lower values. Stability of 16Si02-AIMFI. In order to test the stability of this catalyst, its activity was continuously monitored for 50 h. The catalyst maintained steady-state activity in terms of toluene conversion and selectivity in terms of xylene formed throughout the run of 50 h on stream as illustrated in Figure 4. Kinetic Study. Kinetic runs were carried out in the region free of interparticle diffusion effect. This was established by the runs carried out with constant WIF but varying liquid feed rates. In the case of zeolite-catalyzed reactions two types of diffusion processes are considered (i) macropore between the catalyst pellet particles and (ii) micropore inside the zeolite channels. The above exper-
Ind. Eng. Chem. Res., Vol. 33, No. 2, 1994 249
*Ot
1 1
10
I
I
I
30 40 TIME ON STREAM ( h )
20
I
50
Figure 4. Time on stream behavior of 16SiOz-MFI for selective disproportionation of toluene: (0) toluene conversion, ( X ) p-xylene selectivity. Temperature = 773 K, WHSV = 0.87 h-1; HdHC = 2.
Jx T
3
10
Figure 6. Arrhenius plot for selective disproportionation of toluene using 16SiOz-AlMFI catalyst. Table 3. Activation Energy for Toluene Disproportionation and Selective Toluene Disproportionation Reaction temperature carrier activation energy ref (K) gas (kJ/mol) 723-823 Hz 117 Kaeding et al., 1981 Hz 84 Beltrame et al., 1985 513-573 745-805 Hz 100-121 Bhaskar et al., 1991 723-773 Hz 65 present work
catalyst per hour per mole. Integration of eq 1 gives
W/F
Figure 5. In (1/1- x) vs W/Fplots a t various temperatures using 16SiO~-AlMFIcatalyst. Table 2. Kinetic Parameters for Selective Toluene Disproportionation at Various Temperatures kinetic constant: k (mol h-1 g cat-l atm-I) temperature (K) 723 748 773
16.5 X 103 12.0 x 103 8.25 X
iments for finding the interparticle diffusion region show only the absence of macropore diffusion. Since the channel dimensions of MFI aluminosilicate are comparable to those of reactant toluene and product xylenes and benzene, micropore diffusion resistance cannot be avoided. Hence the kinetic parameters presented here include the diffusional effects. Similar kinetic studies were reported for toluene ethylation (Lee and Wang, 1985), isomerization of ethyl benzene and m-xylene (Hsu et al., 1988), disproportionation of toluene (Chang et al. 1987; Nayak and Riekert, 1986),and methylation of toluene (Mantha et al., 1991). Toluene disproportionation was carried out at three different temperatures over 16Si02-AlMFI catalyst viz. 723, 748, and 773 K in order to collect the kinetic data. A t each temperature WIF was varied to get different toluene conversions. The mole ratio of hydrogen to toluene was kept at 2 in all these experiments. Assuming firstorder dependence of toluene concentration with rate, a model similar to Nayak and Riekert (1986) was proposed: reaction rate = -r = dx/d( WIF) = k(1- x ) (1) where r is the rate of toluene conversion, x is toluene conversion and WIF space time expressed as grams of
In 1/(1-x ) = k(W/F) (2) The rate constant k can be calculated from a plot of In 11(1 - x ) versus WIF. Such plots at three different temperatures are presented in Figure 5. The kinetic parameter values obtained are given in Table 2. The first-order rate constant obtained does not take the deactivation of MFI aluminosilicate due to coke formation into consideration. This is ascribed to a unique feature of the ZSM-5 zeolite which does not allow coke precursor formation, and deposition of coke inside the channels of MFI may not be possible unless the degree of coking is very severe (Bhaskar and Do, 1990). The other reason is our catalyst stability run showed a steady activity without any sign of decrease in conversion with tested time on stream period of 50 h. If the rate constant is expressed in Arrhenius form
k = k, exp(-EIRT) where k, is the frequency factor, E the activation energy, R gas constant, and T the temperature, by plotting In k versus 1/T, activation energy E can be obtained from the slope. This plot is presented in Figure 6. The activation energy obtained from least-squares fitting is presented in Table 3along with activation energies reported for toluene disproportionation in the literature. Our value is lower than those reported by Kaeding et al. (1981a), Beltrame et al. (19851, and Bhaskar and Do (1990). Palekar and Rajadhyaksha (1986) have attributed lower activation energy to an intracrystalline diffusion effect. The same thing seems to be true in our case because, since our zeolite was silylated, the pore opening size entrance dimension became smaller than ZSM-5. Conclusion Any higher p-xylene selectivity desired can be achieved during toluene disproportionation by using appropriately pore-size-controlledMFI aluminosilicate. Silica-deposited zeolite (16 wt % ) exhibited appreciable toluene conversion
250 Ind. Eng. Chem. Res., Vol. 33, No. 2, 1994
of 23 % with 89 7% p-xylene selectivity. With enhancement in reaction temperature from 723 to 803 K toluene conversion and benzene formation increased, while xylene formation decreased. p-Xylene selectivity was affected little up to 773 K, above this temperature it was lowered due to dealkylation. A t higher WHSV of 4.35 h-l, toluene conversion decreased to 9 7%, while para selectivity increased to 93 %. The catalyst showed steady and stable activity and selectivity throughout the run, which was carried out for 50 h. The activation energy calculated assuming first-order rate dependence on toluene conversion was 65 kJ/mol. This value is lower than 84-121 kJ/ mol reported in the literature. This has been explained on the basis of enhanced intracrystalline diffusion effect in the pore-size-regulated MFI zeolite.
Literature Cited Anderson, J. R.; Foger, K.; Mole, T.; Rajadhyaksha, R. A.; Sanders, J. V. Reactions on ZSM-5 type Zeolite Catalysts. J.Catal. 1979, 58, 114. Argauer, R. J.; Landolt, G. R. US. Patent 370, 2886, 1972. Beltrame,P.;Beltrame,P. L.; Cartini, P.; Forni, L.; Zuretti, G. Toluene Disproportionation Catalyzed by various Zeolites. Zeolites 1985, 5,400. Bhaskar, G. V.; Do, D. D. Toluene Disproportionation Reaction over HZSM-5 Zeolites: Kinetics and Mechanism. Znd. Eng. Chem. Res. 1990, 29, 355. Bhavikatti, S. S.; Patwardhan, S. R. Toluene Disproportionation over Aluminium Deficient and Metal-Loaded Mordenites. 1. Catalytic Activity and Aging. Znd. Eng. Chem. Prod. Res. Dev. 1981, 20, 102. Chang, J.-R.; Sheu, F.-C.; Cheng, Y.-M.; Wu, J.-C. Kinetics and Optimization of the Toluene Disproportionation Reaction over Solid Acid Catalysts. Appl. Catal. 1987, 33, 39. Chen, N. Y.; Kaeding, W. W.; Dwyer, F. G. Para-directed Aromatic Reactions over Shape-Selective Molecular Sieve Zeolite Catalysts. J.Am. Chem. Soc. 1979,101,6783. Halgeri, A. B. Disproportionation of Toluene over a Metal Supported type L Zeolite Catalyst. J.Chem. Tech. Biotechnol. 1981,31,591. Halgeri, A. B.; Bhat, Y. S.; Unnikrishnan, S.; Prasada Rao, T. S. R. Para-selective Alkylation of Monoalkyl Benzene over Silylated Gallosilicate Zeolites. Proc. Symp. on Alkylation, Aromatization, Oligomerization and Isomerization of Short Chain Hydrocarbons over Heterogeneous Catalysts, Div. Pet. Chem. Inc., 202nd National Meeting of the American Chemical Society, New York City, Aug. 25-30; American Chemical Society: Washington, DC, 1991. Hibino, T.; Niwa, M.; Murakami, Y. Shape-selectivity over HZSM-5 Modified by Chemical Vapor Deposition of Silicon Alkoxide. J. Catal. 1991, 128, 551. Hsu, Y. S.; Lee, T. Y.; Hu, S. C. Isomerization of Ethylbenzene and m-Xylene on Zeolites. Ind. Eng. Chem. Res. 1988, 27, 942. Kaeding, W. W.; Chu, C.; Young, L. B.; Weinstein B.; Butter, S. A. Shape selective Reactions with Zeolite Catalysts 11. Selective Disproportionation of Toluene to Produce Benzene and p-Xylene. J. Catal. 1981a, 69,392. Kaeding, W. W.; Chu, C.; Young, L. B.; Weinstein, B.; Butter, S. A., Selective Alkylation of Toluene with Methanol to produce Paraxylene. J. Catal. 1981b, 67, 159. Kaeding, W. W.; Young, L. B.; Chu, C. Shape Selective Reactions with Zeolite Catalysts IV. Alkylation of Toluene with Ethylene to produce p-Ethyltoluene. J. Catal. 1984,89, 267. Kim, J. H.; Namba, S.; Yashima, T. Paraselectivity of Pentasil Zeolites. Stud. Surf. Sci. Catal. 1989, 46, 71. Kulkarni, S. J.; Kulkarni, S. B.; Ratnasamy, P.; Hattori, H.; Tanabe, K. The Correlation between Sorption and Catalytic Properties of HZSM-5 type Catalysts. Appl. Catal. 1983,8, 43. Kurschner, U.; Jerschkewitz, H.-G.; Schreier, E.; Volter, J. Shape Selectivity of Hydrothermally treated HZSM-5 in Toluene Disproportionation and Xylene Isomerization. Appl. Catal. 1990,57, 167. Lee, B. J.; Wang, I. Kinetic Analysis of Ethylation of Toluene on HZSM-5. Znd. Eng. Chem. Prod. Res. Dev. 1985, 24, 101. Leu, L. J.; Kang, B. C.; Wu, S. T.; Wu, J. C. Toluene Disproportionation Reaction over Modified HY and LaHY Catalysts. Appl. Catal. 1990, 63, 91.
Lonyi, F.; Engelhardt, J.; Kallo D. Influence of the Tortuosity and the Acidity of HZSM-5 on the Selectivities in Ethylation of Toluene. Stud. Surf. Sci. Catal. 1989, 49, 1357. Mantha, R.; Bhatia, S.; Rao, M. S. Kinetics of Deactivation of Methylation of Toluene over HZSM-5 andH-Mordenite Catalysts. Znd. Eng. Chem. Res. 1991,30, 281. Mavrodinova, V.; Minecher, Ch.; Penchev, V.; Lechert, H. Toluene Conversion over Offretite, Omega and ZSM-5. Zeolites 1985, 5, 217. Meisel, S. L.; McCullough, J. P.; Lechthaler, C. H.; Weisz, P. B. Recent Advances in Production of Fuel and Chemicals over Zeolite Catalysts, Leo Friend Symp., 174th National Meeting of the American Chemical Society, Chicago, IL, Fall 1977; American Chemical Society: Washington, DC, 1977. Meshram, N. R. Selective Toluene Disproportionation Over ZSM-5 Zeolites. J. Chem. Tech. Biotechnol. 1987, 37, 111. Meshram, N. R.; Hegde, S. G.; Kulkarni, S. B.; Ratnasamy, P. Disproportionation of toluene over HZSM-5 Zeolites. Appl. Catal. 1983, 8, 359. Murakami, Y., Super Selective Catalysis by CVD Zeolites. Stud. Surf. Sci. Catal. 1989, 44, 177. Nayak, V. S.;Riekert, L. Catalytic Activity and Product Distribution in Disproportionation of Toluene on Different Preparations of Pentasil Zeolite Catalysts. Appl. Catal. 1986,23,403. Niwa, M.; Itoh, H.; Kato, S.;Hattori, T.; Murakami, Y. Modification of H-Mordenite by a Vapor Phase Deposition Method. J. Chem. Soc., Chem. Commun. 1982,819. Nunan, J.; Cronin, J.; Cunningham, J. Combined Catalytic and Infrared Study of the Modification of HZSM-5 with Selected Poisons to give high p-Xylene Selectivity. J. Catal. 1984,87, 77. Oliver, E. D.; Inoue, T. Aromatics BTX. Stanford ResearchZnstitute Handbook; No. 30A; SRI International: CA, 1970. Olson, D. H.; Hagg, W. 0.Structure Selectivity Relationship in Xylene Isomerization and Selective Toluene Disproportionation. Catalytic Materials Relationship Between Stucture and Reactivity. ACS Symposium Series 248; American Chemical Society: Washington, DC, 1984; p 275. Palekar, M. G.; Rajadhyaksha, R. A. Sorption Accompanied by Chemical Reactions on Zeolites. Catal. Rev.-Sci. Eng. 1986, 28 (4), 371. Paparatto, G.; Moretti, E.; Leofanti, G.; Gatti, F. Toluene Ethylation on ZSM Zeolites. J. Catal. 1987, 105, 227. Paparatto, G.; de Alberti, G.; Leofanti, G.; Padovan, M. The Role of the External Surface in Reactions with Zeolite Catalysts. Stud. Surf. Sci. Catal. 1989,44, 255. Ribeiro, M. F.; Ribeiro, F. R. Influenceof Si/AlRatioon the Catalytic Properties of Ni-H Mordenites in the Disproportionation of Toluene. J. Mol. Catal. 1987, 39. 269. Schulz-Ekloff, G.; Jaeger, N. I. Effects of Carrier Gasesin the Toluene Disproportionation on HZSM-5 Zeolite. Appl. Catal. 1987,33,73. Uguina, M. A.; Sotelo, J. L.; Serrano, D. P. Toluene Disproportionation over ZSM-5 Zeolite: Effects of Crystal Size, Silicon to Aluminium Ratio, Activation Method and Pelletization. Appl. Catal. 1991, 76, 183. Uguina, M. A,; Sotelo, J. L.; Serrano, D. P.; Grieken, R. V. Magnesium and Silicon as ZSM-5 Modifier Agents for Selective Toluene Disproportionation. Znd. Eng. Chem. Res. 1992, 31, 1875. Uguina, M. A.; Sotelo, J. L.; Serrano, D. P. Kinetics of Toluene Disproportionation over Unmodified and Modified ZSM-5 Zeolites. Znd. Eng. Chem. Res. 1993, 32, 49. Vayssilov, G.; Yankov, M.; Hamid, A. Para Selective Alkylation of Toluene with Methanol over ZSM-5 Zeolite. Appl. Catal. 1993, 94, 117. Wang, I.; Ay, C . L.; Lee, B. J.; Chen, M. H. Selectivation of p-dialkyl benzene with In-situ Vapor Phase Modification of HZSM-5.9th Int. Congr. Catal. Calgary, Canada 1988, 324. Yashima, T.; Sakaguchi, Y.; Namba, S. Selectve Formation of p-Xylene by Alkylation of Toluene with Methanol on ZSM-5 type Zeolites. Stud. Surf. Sci. Catal. 1981, 7, 739. Young, L. B.; Butter, S. A.; Kaeding, W. W. Selectivity in Xylene Isomerization, Toluene-Methanol alkylation and Toluene Disproportionation over ZSM-5 Zeolite Catalysts. J.Catal. 1982, 76, 418. Received for review May 4, 1993 Accepted October 5, 1993 *
* Abstract published in Advance ACS Abstracts, December 15, 1993.
